BONE-MINERAL LOSS DURING LACTATION AND RECOVERY AFTER WEANING

Objective: To test the hypothesis that bone mineral content (BMC) and density (BMD) are lost during lactation and regained within 6 months a fter weaning. Methods: Two cohorts of women, defined by time postpartu m were enrolled into the study; each cohort was followed for 6 months. Women in the lactation cohort (65 lactating women and 48 nonlactating postpartum controls) were enrolled at 2 weeks postpartum. Women in th e weaning cohort (40 lactating and 43 nonlactating postpartum controls ) were enrolled at 4-6 months postpartum. Lactating women enrolled in the weaning cohort had been fully breast-feeding at enrollment and wea ned within 2 months of enrollment Bone mineral. content of the total b ody and BMD of the lumbar spine and distal radius were measured by dua l-energy x-ray absorptiometry. Results: Lactating women lost significa ntly more bone in the total body (-2:8 versus -1.7%) and lumbar spine (-3.9 versus 1.5%) than did nonlactating women during the first 6 mont hs postpartum. There was no effect of lactation on bone changes at the distal radius. After weaning, lactating women gained significantly mo re bone in the lumbar spine than did nonlactating women (5.5 Versus 1. 8%). Earlier resumption of menses was associated with a smaller loss o f bone during lactation and a greater increase of bone after weaning. Conclusion: Women lose bone during lactation but gain bone after weani ng. Thus, lactation may not result in net bone loss.